Ventilators are commonly used to supply air or air enriched with oxygen to the lungs of a person having difficulty breathing on his own. Typically, such individuals either cannot breathe by themselves or are only able to breathe insufficient amounts of air on their own Still others can breathe normally some of the time but irregularly and insufficiently at other times. Consequently, ventilators are used in some cases constantly by the individual whereas in other cases, they are utilized only occasionally as for example while sleeping if there is a significant possibility the individual may lapse into a state where he fails to breathe involuntarily.
Virtually all ventilators include pumps that are capable of delivering a selected volume of air under a selected pressure for a selected time duration and at selected time intervals to a person. Ideally, a ventilator's operating parameters may be very sensitively adjusted to fulfill the unique respiratory needs of a particular person. In some instances, a ventilator may be utilized to wean a person from reliance on artificial respiration to a state where he independently and reliably respirates. In such a mode of operation, the ventilator supplies pressurized air to the person at infrequent time intervals to encourage the person to independently respirate but will provide sufficient artificial respiration to the person in the event he fails to do so. A ventilator in this mode of operation preferably includes means for sensing the independent respiration of the person and for actuating an alarm signal if the independent respiration falls below a selected frequency.
Most ventilators heretofore utilized have included an electric motor operatively connected through a complex crank arm assembly to a piston contained within a cylinder In the operation of such ventilators, air is drawn into the cylinder through an inlet port as the piston is moved in one direction within the cylinder whereupon the movement of the piston is then reversed to compress the air and force it through an outlet port in the cylinder to the patient. The crank arm assemblies utilized in such ventilators are relatively complex primarily because of the need to vary the stroke length of the piston so that a selected, variable quantity of air may be supplied to the patient. Moreover, such crank arm assemblies tend to be relatively bulky and noisy in operation which are highly undesirable traits in a portable ventilator where space is at a premium and quietness of operation is greatly preferred.
The present invention dispenses with a crank arm assembly and replaces it with a threaded, rotatable shaft. The shaft is driven by a motor and the piston moves within the cylinder in response to the rotation of the threaded shaft. The ventilator of the present invention is relatively simple and compact in construction and quiet in operation.
A patentability search was conducted for the present invention and the following patents were developed:
______________________________________ U.S. Pat. No. Inventor Issue Date ______________________________________ 3,208,388 Glasgow September 28, 1965 3,225,758 Morch December 28, 1965 3,651,804 Spiller March 28, 1972 3,658,443 Fumagalli April 25, 1972 4,014,415 Pickel March 29, 1977 4,022,076 Metz May 10, 1977 4,145,165 Perkins et al. March 20, 1979 4,155,356 Venegas May 22, 1979 4,262,667 Grant April 21, 1981 4,276,003 Perkins et al. June 30, 1981 ______________________________________
Of these patents, the Glasgow patent is believed to be the most relevant as it discloses a piston-cylinder type of pump in which the piston is reciprocated by a ball nut mounted on a threaded shaft. However, as best seen in Glasglow's FIGS. 2 and 5, his threaded shaft is positioned externally of his cylinder adding size to his pump in contrast to the present invention in which the shaft is positioned within the cylinder and passes through an aperature in the piston itself.
The inventors are also aware of a device manufactured by North American Phillips Company for transforming rotational motion into translational motion. The device includes an electric motor provided with a longitudinally hollowed armature. A ball bearing nut is mounted on the armature and operatively contacts a threaded shaft extending through the armature. Operation of the electric motor. causes a rotation of the armature and ball bearing nut, which causes a concurrent translation of the threaded shaft